It is planned to initiate a National Simulation Resource for Stochastic Population Models. In its early phases, this Resource is referred to as a Preresource. Hardware and software will be assembled to enable convenient, human-oriented studies of stochastic population models. The simulation programs will be modifications of the current system, VESPERS-11, used to simulate influenza epidemics and the effects of vaccination strategies and other public health measures. VESPERS-11 is highly modularized; it can be adapted to the simulation of quite different stochastic population models by changing a limited number of program modules. The simulation programs will be tested for functionality by core research studies of models of: 1) epidemics of infectious diseases and vaccination; 2) chronic diseases, including intervention and prevention strategies; 3) genetics and human disease. The results of these simulations will be of interest in themselves, as will the outcomes of the collaborative studies which, for the Simulation Preresource, will test the user-friendliness of its offerings. As the Preresource matures towards a full Resource, service will be supplied to local and remote research groups. The Preresource will be used for training graduate students, medical residents, and post-doctoral students. The existence of the Resource, its potential utility, and its research results will be disseminated by oral presentations at technical meetings, by journal articles, and by the publication of user manuals.